1. Technical Field
The present invention relates to a fiber optic cable; and more particularly to a fiber protection sleeve assembly for use in a splice junction of a fiber optic cable.
2. Description of Related Art
Over the years, fiber optic cables have gained popularity and are used in a variety of fields. One such field is oil and gas exploration where fiber optic systems, such as that shown in FIG. 1, are used for measuring various conditions underground, such as temperature, pressure, acceleration and vibration. A gas and/or oil exploration environment is harsh, characterized by well gases and fluids, extreme temperatures and pressures, and multiple other cables and equipment extending downwardly through a well into a deep underground region.
FIG. 1 shows one such system 10 for detecting the various conditions in an underground region 12 and transmitting data indicating the status of those conditions to the surface 14 that includes a fiber optic cable 16 having a surface end 20 and an underground end 22. The surface end 20 of the fiber optic cable 16 attaches to an instrumentation box 24 on the surface 14, while the underground end 22 extends into the underground region 12, passing through a well 26 and supporting one or more measuring devices 28. The fiber optic cable 16 has one or more optical fibers that are typically fragile and must be shielded from the harsh well environment. To effectively protect the optical fiber from the well environment, the optical fiber is placed into protective metal tubing and is environmentally sealed therein, like that shown in FIGS. 2 and 3.
FIGS. 2 and 3 show the fiber optic cable 16 which has optical fibers 32, 33 ultimately shielded by a protective outer capillary tube 34. Typically, the optical fibers 32, 33 are encased in a thin layer of flexible coating 35. The optical fibers 32, 33 are affixed to the inner capillary tube 37 using a pliable material 36, such as grease for example. A blocking polymer 38 is disposed between inner capillary tube 37 and outer capillary tube 34. The fiber optic cable 16 ensures that the optical fibers 32, 33 are protected from the harsh environment and from any mechanical loads imparted on the fiber optic cable 16. The subject matter of FIGS. 1, 2 and 3 is shown and described in more detail in a commonly-owned co-pending United States Patent Application, filed with Express Mail No. EL419975708US on Feb. 3, 2000 also hereby incorporated by reference in its entirety. Also see commonly-owned copending U.S. patent application Ser. No. 09/121,468, hereby incorporated by reference in its entirety, for a detailed description of another such optical fiber cable.
During installation and maintenance of the system 10 in FIG. 1, segments of the fiber optic cable 16 must be joined and sealed to form and maintain a continuous protective covering for the optical fibers 32, 33. For example, when the fiber optic cable 16 is either connected to another fiber optic cable, terminated on either end at a well head, a junction box or other instrument, or spliced and repaired for any other reason at some intermediate cable point, the metal inner and outer capillary tubes 34, 37 are cut and opened to gain access to the optical fibers 32, 33. After splicing the optical fibers 32, 33 to other optical fibers, ends of the metal inner and outer capillary tubes 34, 37 must be joined together or terminated at a splice junction.
By way of example, FIG. 4 shows a splice junction for a fiber optic cable 42 that is set forth in the commonly-owned co-pending United States Patent Application, filed with Express Mail No. EL419975708US on Feb. 3, 2000. In summary, the fiber optic cable and splice junction includes the optical fibers 32, 33, the outer capillary tube 34, a buffer material 36, the capillary tube 37, a blocking polymer 38, a splice protection assembly generally indicated as 40, slice couplings 46, 48, an outer tube 50, welds 52, 54, 56, 58, carrier tubes or heat sink tubes 60, 62, swage crimps 64, 66, swage crimps 80, 82, a splice protection 91, a splice area 144, and fiber splices 148, 150.
During installation and maintenance of the system 10 in FIG. 1, segments of the fiber optic cable 16 must also be cut and opened to gain access to the optical fibers 32, 33. There are known methods in the art of cutting and opening the metal inner and outer capillary tubes 34, 37 to gain access to the optical fibers 32, 33. In particular, the focus of this patent application is on the cutting and opening of the metal inner capillary tube 37, which is a metal tube about 2.4 millimeters in diameter. Typically, a knife file is used to provide a radial score on the metal inner capillary tube 37, which is then flexed until it breaks-off to expose the optical fibers 32, 33.
However, when the metal inner capillary tubes 34, 37 are cut and opened to gain access to the optical fibers 32, 33, then reassembled, problems arise due to the potential for cutting of the fiber jacket 35 caused by exposed edges of the capillary tube 37, when the spliced junction of the fiber optic cable 16 is subjected to vibration.
Because of this, various scoring, breaking and deburring tests were conducted by the inventor. In one test, visual inspections of the tube samples showed that a broken end of the metal inner capillary tube 37 was deformed with varying degrees of metal wings or tabs by the separation process. The deeper the score of the tube, the greater likelihood of a thin xe2x80x9ctab or wingxe2x80x9d of metal being produced. This xe2x80x9ctab or wingxe2x80x9d of metal may be bent either inwardly, outwardly or both. Any surface obstruction or restriction of the inner diameter of the broken end of the metal inner capillary tube 37 will pose a threat for fiber damage by abrasion over time. All samples exhibited this type of result to some extent.
In a second test, the samples were visually inspected after the deburring of the metal inner capillary tube 37. The inner diameter of the metal inner capillary tube 37 was opened by the deburring tool, but there was evidence of metal wings or tabs still present. A review of the separation process indicated that the metal inner capillary tube 37 had a tendency to rotate or twist with the deburring tool as it was being applied. This reduced the effectiveness of the deburring tool to remove the burrs, as did the rocking motion that is required to prevent possible fiber twist damage due to the tight inner diameter of the tool on the fiber. The combination of the twist, the required tightness of the inner diameter of the tool and the tool geometry (hex outer diameter surface) resulted in a poor end preparation of the inner tube 37, that could cause fiber damage.
In a third test, samples were visually inspected after the deburring of the metal inner capillary tube 37 held stationary. The inner diameter of the metal inner capillary tube 37 was opened and clear, but the deburring tool produced a counter bore on the inner diameter and flared the end of the outer diameter, i.e. the xe2x80x9ctab or wingsxe2x80x9d were bent outward. This flare is a more favorable condition for the fiber interface; however, it does pose a problem with the splice procedure, because the copper heatsink centering washer will not pass over the flare.
These tests indicate that the aforementioned splicing procedure may present a reasonable risk of damage to the optical fibers 32, 33 in the spliced junction of the fiber optic cable 16. Failure of the transmission of optical signals on the optical fibers 32, 33 would be catastrophic to the performance of a signal transmission system like the system 10 shown in FIG. 1.
The present invention features a fiber protection sleeve assembly and method for installing the same in a splice junction of a fiber optic cable, which reduces any likelihood of damage to optical fibers in the fiber optic cable caused by vibration or shock after assembly.
The fiber protection sleeve assembly is for use in a fiber optic cable, including a splice junction, having a capillary tube with a capillary tube end and having an optical fiber arranged therein and extending therefrom, and includes at least a first tube, and may include a second tube and a third tube.
The first tube is partially arranged in the capillary tube end and has a bore for allowing the optical fiber to pass through and for preventing contact between the capillary tube end and the optical fiber. The first tube may be a polymeric material, a thermoset or thermoplastic material, and in one embodiment is an orange polyimide tube about one inch long. The material of the first tube should be rigid enough to be slipped inside the capillary tube end and compliant enough to protect the optical fiber. The first tube may be positioned and held in place either by tabs/burrs on the capillary tube end or by a secondary crimping operation.
In another embodiment, the second tube frictionally engages the first tube for arranging the first tube in relation to the capillary tube end and has a bore for allowing the optical fiber to pass through, for example, for splicing to another optical fiber. The second tube may be a polymeric material, an elastomeric material, and in one embodiment is a clear silicone tube about two inches long.
The fiber protection sleeve assembly may also include a third tube for arranging and crimping to a carrier tube of the fiber optic cable to abut the second tube against the capillary tube end and has a bore to allow the optical fiber to pass through, for example for splicing to another optical fiber. The third tube may be a polymeric material, an elastomeric material and in one embodiment is an orange silicone tube about one inch long.
Embodiments are also envisioned wherein the second tube is arranged and crimped in a carrier tube of the fiber optic cable to seal the optical fiber and abut the second tube against the capillary tube end, eliminating the need for the third tube.
The method for protecting the fiber optic cable includes the steps of: (1) inserting a first tube partially into a second tube to form a fiber protection sleeve assembly; (2) sliding the optical fiber through the fiber protection sleeve assembly; (3) inserting the first tube into the capillary tube with the fiber protection sleeve assembly contacting the capillary tube end; (4) installing a carrier tube over the fiber protector assembly and crimping the carrier tube on the capillary tube; (5) passing the optical fiber through a third tube; and (6) inserting the third tube into the carrier tube, and crimping the carrier tube on the third tube to seal the fiber and arrange the first tube in relation to the capillary tube end.
The invention also relates to a fiber optic cable having such a fiber protection sleeve assembly.
The fiber protection sleeve assembly and method of installing the same can be used when the fiber optic cable is either connected to another fiber optic cable (not shown), terminated on either end to a well head, a junction box or other instrument, or spliced and repaired for any other reason at some intermediate cable point, where the metal inner and outer capillary tubes are cut and opened to gain access to the optical fiber.
The foregoing and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing.